Polyamide filament



States Pate This invention relates to synthetic textile fibers and more particularly to the production of crimp'able filaments having a high degree of crimp reversibility.

It is known in the art-that drawn, composite filaments containing eccentric, differential shrinkage components,

either in a side-by-side or a sheath'core relationship, develop a helical crimp when boiled on. Although such resultfinjhe development of improved bulk, covering power and handle in the fabric.

. EXAMPLE I The salt of p-xylylene dia'min'e and azelaic acid is made by preparing an 11% by weight solution. of azelaic acid in methanol in a stainless steel container and adding an 'equimolar quantity of p-xylylene diamine in the form of tated for. 5, minutes after which the salt is filtered oil,

filaments have contributed substantially to the production of fabrics of improved aesthetics, further improvements are desired, particularly with respect to the bulk, covering power and handle of the fabrics.

Additionally, crimped composite fibers having'the characteristic of decreasing the amount of crimp when exposed to, a swelling agent and reverting to the original crimp upon removal of the swelling agent have been disclosed by Breen in US. 3,038,236. Although such crimp reversibility is responsible for some improvement in fabric bulk and covering power, the need for additional improvements is apparent, particularly withregard to the low crimping force exhibited by known high modulus, hydrophobic, composite fibers.

It is accordingly the most important object of this in vention to provide an improved, reversible crimp filament characterized by a substantial increase in crimping force. A corollary objective is to provide a crimpable fiber, the use of which facilitates production of fabrics having improved bulk, covering power and handle.

These and other objectives are accomplished in a drawn, crimpable, composite filament including at least two continuous, adherent, polyamide components which are adapted to shrink difiercntially and thereby crimp as the filament first cools from a temperature of about 230 C. Thereafter, one of the components elongates reversibly and the other shrinks reversibly during each of several heating-cooling cycles. This novel combination of properties insures a crimped length contraction of at least 15% under a load of 0.0015 gram/denier each time the filament is cooled from 230 C.

Such a filament is prepared by melt extruding at least two components either in a side-by-side or a sheath-core relationship, the first cpmponcnt having, when extruded and drawn separately, a reversible thermal. expansion at 230 C. of at least 0.75%. This component is a fiberforming polyamide prepared trom an aliphatic dicarboxylic acid and p-xylylene diamine (PXD) or a mixture of diamines containing at least 75% PXD. As noted previously, the other component, when extruded and drawn separately, shrinks reversibly during a similar heatingcooling cycle. The first component has a substantially greater initial shrinkage capacity and is thus the loadbearing component.

It has been found that crystalline, oriented filaments from the fiber-forming PXD polymers undergo reversible expansion to a'high degree when the filament is heated. Thus, when the PXD polymer is used in a two-component filament with another polyamide which not only has a lower shrinkage but also the capabilityof shrinking rewashed with methanol and dried in a vacuum oven at a temperature of 80 C. for 60 hours.

The above salt, in the amount of 10,000 grams, is charged into an autoclave together with 10,000 grams of water, 30 grams of acetic acid and 125 grams of p-xy1ylene diamine. The autoclave is purged with nitrogen and heated rapidly to a temperature of 210 C. When the temperature reaches 200 C., 133 grams of 20% titanium dioxide delusterant slurry is added with agitation. After the temperature reaches 210 C., the temperature and pressure are maintained for 1 hour. The temperature is then raised to 250 C. andthe pressure: to 300 psi. over a period of 30 minutes, after which the temperature is raised to 285 C. and the pressure reduced to atmospheric over a period of minutes, this condition being main tained for an additional period of 2hours.

' The polymer. (PXD-9) is discharged from the autoclave and cut into flake as'de'scribed in U.S. 2,289,774. The flake has an inherent viscosity of 0.72.

Polyhexamethylene adipamide (66 nylon) flake having a relative viscosity of 45 is prepared in the conventional manner. The 6-6 and PXD-9 flakes are melted separately in screw melters and then extruded in continuous, adherent,-'side-by-side relation from 34 holes in a spinneret of the type shown in FIG. f US. 2,931,091 to produce composite .filame'nts in which the two components are present in an approximately 1:1 weight ratio. The freshly spun filaments are quenched by passing air transversely across the bundle, as described in US. 2,273,105, and then wound into a package in the conventional manner. The

. yarn is subsequently drawn, as shown in US. 2,289,232,

on a draw-twister, the draw ratio being 4. The denier of the helix. The reversible loss and gain of crimp or versibly in subsequent heating-cooling cycles, that fila "squirm' in the yarn is measured by heating the dry, crimped yam to 230 C. and again cooling to 25 C. The percent squirm under no restraint andunder various degrees of slight restraint is determined by suspending crimped' samples in a closed, electrically heated tube, measuring their length, heating the samples to 230 (3., measuring, cooling to 25 C. and again measuring sample lengths. The squirm-ability reported in Table l is calculated from the various measurements. Where reported, the indicated loads were attached to the free ends before heating the crimped'samples to 230 C. For comparison, results obtained with severalother two-component yarns are also shown, fiber A being a two-component yarn in which one component is poly(m-xylylene adipamide') (MXD-6) and the other component is 6-6 nylon, fiber B a two-component yarn in which one component is poly- (ethyleneterephthalate) and the other'component is 6-6 nylon and fiber C atwo-cornponent yarn in which one component is the polymer derived from bis-p-amino-cyc1ohexylmethane'and azelaic acid and the other component is tit-6 nylon.

' disclosed by Breen in US.

' separately, the yarn shrinks 17% denier,

. ious PXD polymers and copolymers mer containing 90% When swelled and dried according to the procedures 3,038,236, the crimped PXD- elongated and contracted by Under a load of 0.001 g.p.d.,

9/6-6 composite filament only 18% under no load.

onlya 12% squirmwas observ Whenthe PXD-9 component is extruded and drawn when initially heated to 230 C. and then cooled to 25 C. Thereafter, the yarn expands 1.3% in length upon heating to 230 C. and contracts to its original shrunk length-upon cooling to 25 C. I The 6-6 component, when treated in this fashion, shrinks 12% initially and, upon subsequent heating and cooling, shrinks 1.8% and then length. Repeated heating-cooling cycles show these thermal expansion and shrinkage characteristics to be permanently reversible.

Uncrimped yarn, prepared as described above, is crirnped at 232 C. and knit tubing is prepared from the yarn in the conventional manner. The tubing is repeatedly oven heated to 230 C. and cooled to room temperature. After three cycles, a substantial improvement in bulk, covering power and hand is noted. By comparison, tubings knittedfrom crimped fibers A, B and treated similarly show far less improvement.

. EXAMPLEII Two-component, 30 denier, 10 filament, 'PXD-9/6-6 yarn is prepared as described in Example I. The drawn, uncrimpedyarn is coned and knitted into a 32 inch, 28 gauge, .15 quality jersey tricot fabric which is subjected to a conventional scour, oven dried at 120 C. and heated at 210 C. in a relaxed state to develop crimp. After cooling, the fabric has considerable bulk because of the crimping action. A portion of the bulked fabric is heated repeatedly to 230 C. followed by cooling to room' temperature. After three cycles, it is further improved in covering power, bulk and hand.

. EXAMPLEIH Following the general procedure of Example I, 70 34. filament, side-by-side, two-component yarns are prepared with 6-6 nylon as one component and varas the other component. These included p-xylylene adipamide, the copolyp-xylylene azelamide and 10% mxylylene azelamide and the copolymer containing 75% 'p-xylylene azelamide and 25% m-xylylene azelamide. The two-component yarns-containing other PXD polymers and copolymers exhibit about the same reversible expansion when heated to 232 C. as the two-component yarn containing PXD-9 (Example I). When these yarns are knittedinto fabrics, the results are substantially the same as found in Example I.

As indicated in the foregoing examples, the crimpable yarn of this invention may be utilized in fabrics, particularly knit fabrics, to produce a very desirable improvement in bulk, covering power and hand.

The crimped fibers of this invention are unique in that the load-bearing component exhibits a high degree of thermal expansion. Consequently, the fibers not only lose crimp when heated but also have the ability to contract or re-crimp on cooling against restraining forces which prevent prior art fibers from contracting to such' an extent. As shown irrTable I, a two-component filament (fiber C) in which the high shrinkage component is 6-6 elongates to its original nylon and the other component is polyethylene terephthalate, i.e., a fiber of the same composition disclosed in Examples 11 and III of U.S. Patent No. 3,038,236 to Breen, shows about the same retraction under no restraint as the fib'er of this invention but, under a load of 0.001 g.p.d. (a degree of restraint which exists in fabrics), the instant fiber'has a five-fold advantage. Even in comparison with a two-component fiber from 6-6 nylon and an MXD polyamide (fiber A, Example I), the fibers of this invention show a two-fold advantage.

To obtain the results disclosed herein,- one component of the composite filament should have a reversible thermal expansion of at least 0.75%, the extended length of the fiber before expansion, when heated to 230 C. and subsequently cooled to 25 C. under a restraint of 0.001 g.p.d., i.e., the polymeric material in that one component, when extruded and drawn separately, must expand at least 0.75% when heated and then contract to substantially its shrunk length under a restrainingload of 0.001 g p.d. This component must also have a higher shrinkage than the other components in the fiber when initially heated to 230 C. and then cooled. In this connection, it should be noted that the high'shrinkage polyamide components disclosed by Breen, e.g., 6-6 nylon in Examples 11 and In of US. 3,038,236, are not thermally expansible. The preferred'polymeric materials for use as the high shrinkage component are those derived from p-xylylene diamine and aliphatic dicarboxylic acids. Suitable aliphatic acids include adipic acid, suberic acid, sebacic acid, undecan-dioic acid, and dodecan-dioic acid. A mixed acid containing up to 25% of another aliphatic acid or of a non-aliphatic acid such as isophthalic acid or terephthalic acid may be .employed. Copolymers containing up to about 25% of another diamine may also be .employed.

The other component or components in the fiber may consist of any other synthetic linear fiber-forming polyamide having a relatively low initial shrinkage upon cooling from a temperature of about 230 C. As against thermal expansibility, this component should shrink repolymers includes 6-6 nylon, 6 rnylon,

' 'oxamide, polyhexamethylene sebacamide and various copolymers.

In order to obtain the improvements of this invention, the thermally expansible component must have the higher initial shrinkage, i.e., it must be the load bearing component in the crimped fiber. In order to accomplish this, it must be prepared from a polymer having a molecular weight in the fiber-forming range. If lower molecular weight polymers are employed, this component does not have the higher shrinkage of the two components and the desired product is not obtained.

In order to perform satisfactorily, the fibers of. this invention must, of course, be drawn and the orientation so produced must be-substantially retained after the heating' and cooling treatment which is necessary to produce therequisite thermal squirm. Undrawn fibers or fibers which become deoriented on heating (e.g., fiber C, Example I) are not satisfactory.

Having thus described the invention, what isclaiined as new and desired to be securedby Letters Patent is:

1. A drawn, crimpable, composite filament comprising two continuous, adherent, polyamide components adapted to shrink differentially and thereby crimp as the fil"- ment first cools from an elevated temperature, one of said components being adapted to elongate reversibly and the other to shrink reversibly in subsequent heatingcooling cycles, said one component being of fiber-forming molecular weight and also having aninitial shrinkage potential relatively higher than that of the other component.

2. The crimpable filament of claim 1 wherein said one component comprises the polyamide prepared from p-xylene diamine and an aliphatic dicarboxylic acid.

preferably 1.0%, based on 3. The crimpahle fiiament of clainrl wherein said one component consists essentially of the polyaniid'e prepared from p-xylcne diamine and an aliphatic dicarboxylic acid. l

4. The crimpable filament of claim'. 3 wherein said other component consists essentially of a polyamide selected from the group consisting of polyhexamethylene adipamide, polycaproamide, polyoctamethylene oxamide, polyhcxaxnethylene sebacamide and copolyamides thereof.

5. A nmwn, crimpable, composite filament comprising continuous, adherent components of fiber-forming holyp-xylylene azelamide and polyhexamethylene adipamide.

6. A drawn, criinped, composite filament comprising two continuous, adherent, polyamide components, one

a a crimped, length contraction of at least 15% upon coolof said components being adapted to elongate reversibly 15 and the or to shrink reversibly in repeated heatingingirom 230 C. under a load of 0.0015 gram/denier.

1. A fabric containing a plurality of filaments of claim 6.

8. A fabric containing crimped, composite, squirmahle filaments each comprising continuous, adherent components of fiber-forming noly-p xylylene azelamide and polyhexamethylene adipamide, sairi filaments being characterized by va crimpcd length contraction of at least 15% upon cooling from 230 C.

References Cited in the n; of this patent .UNITED STATES PATENTS 2,931,091 Bt ecn Apr. 5, 1960 

1. A DRAWN, CRIMPABLE, COMPOSITE FILAMENT COMPRISING TWO CONTINUOUS, ADHERENT, POLYAMIDE COMPONENTS ADAPTED TO SHRINK DIFFERENTIALLY AND THEREBY CRIMP AS THE FILAMENT FIRST COOLS FROM AN ELEVATED TEMPERATURE, ONE OF SAID COMPONENTS BEING ADAPTED TO ELONGATE REVERSIBLY AND THE OTHER TO SHRING REVERSIBLY IN SUBSEQUENT HEATINGCOOLING CYCLES, SAID ONE COMPONENT BEING OF FIBER-FORMING MOLECULAR WEIGHT AND ALSO HAVING AN INITIAL SHRINKAGE POTENTIAL RELATIVELY HIGHER THAN THAT OF THE OTHER COMPONENT. 